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70 


BULLETIN  NO.  248 


A  MODIFICATION  OF  THE  BABCOCK 

TEST  FOR  THE  DETERMINATION 

OF  FAT  IN  BUTTERMILK 

BY  P.  H.  TRACY  AND  O.  R.  OVERMAN 


URBANA,  ILLINOIS,  JANUARY,  1924 


A  MODIFICATION  OF  THE  BABCOCK  TEST  FOR 

THE  DETERMINATION  OF  FAT  IN 

BUTTERMILK 

BY  P.  H.  TRACY,  FIRST  ASSISTANT  IN  DAIRY  MANUFACTURES,  AND 
O.  E.  OVERMAN,  ASSISTANT  CHIEF  IN  DAIRY  CHEMISTRY 

An  accurate  method  for  the  determination  of  fat  in  buttermilk  is 
necessary  in  order  to  control  the  exhaustiveness  of  the  churning  proc- 
ess. The  testing  equipment  in  creameries  usually  consists  of  a  Bab- 
cock  test  outfit,  which  affords  a  cheap  and  rapid  method  for  the  de- 
termination of  fat  in  milk  products.  Certain  procedures  have  been 
developed  and  certain  types  of  test  bottles  have  been  produced  for 
testing  whole  milk  and  cream,  but  for  buttermilk  the  present  Babcock 
method  has  not  proved  satisfactory,  nor  is  there  an  adequate  test 
bottle.  Buttermilk  is  tested  in  the  ordinary  18-gram  skim-milk  bottle, 
which  is  graduated  from  0.0  to  0.25  of  one  percent  (a  few  bottles 
graduated  from  0.0  to  0.50  of  one  percent  are  being  put  on  the  market) , 
whereas  the  amount  of  fat  in  buttermilk  will,  in  some  cases,  exceed 
one  percent. 

This  bulletin  describes  an  attempt  to  devise  a  modification  of  the 
Babcock  method  that  will  prove  more  satisfactory  than  the  present 
method.  The  experiment  was  so  conducted  as  to  obtain  information 
on  the  following  points: 

A.  The  conditions  limiting  the  use  of  the  Babcock  test  for  butter- 
milk. 

3.     The  amount  of  sulfuric  acid  used. 

2.  The  time  of  centrifuging. 

3.  The  speed  of  centrifuging. 

B.  A  comparison  of  the  Babcock,  normal  butyl  alcohol,1  and  Roese- 
Gottlieb  methods  for  determining  the  amount  of  fat  in  buttermilk. 

METHOD  OF  PROCEDURE 

The  buttermilk  used  in  the  experimental  work  was  obtained  from 
the  churning  of  neutralized  cream  in  a  Dual  churn  and  worker.2 

All  the  Babcock  and  normal  butyl  alcohol  tests  were  conducted  in 
an  electric  centrifuge  having  a  22-inch  disc  and  a  speed  adjustment 
ranging  from  850  to  1700  revolutions  per  minute. 


JChicago  Dairy  Produce,  December  31,  1921. 

•With   the   exception   of   sample   No.   12,   Table  4,   which   was  hand-churned 
buttermilk. 

64 


MODIFIED  BABCOCK  TEST  FOR  FAT  IN  BUTTERMILK  ti5 

The  acid  was  measured  directly  into  the  test  bottle  from  a  burette, 
as  it  was  found  that  accurate  measurements  could  not  be  obtained  by 
the  use  of  an  acid  measure  or  graduated  cylinder.  The  sulfuric  acid 
used  had  a  specific  gravity  of  1.83. 

Skim-milk  bottles  graduated  from  0.0  to  0.50  of  one  percent  were 
used  for  the  normal  butyl  alcohol  tests,  and  bottles  graduated  to  0.25 
of  one  percent  were  used  for  the  Babcock  tests. 

ROESE-GOTTLIEB    DETERMINATIONS 

In  general,  the  procedure  as  given  by  the  Association  of  Official 
Agricultural  Chemists1  was  followed  in  the  Roese-Gottlieb  determina- 
tions. Three  extractions  with  ether  were  made  in  each  case.  It  was 
found  necessary  to  use  more  ammonia  than  is  needed  in  testing  other 
milk  products,  and  it  was  often  necessary  to  add  ammonia  in  the  sec- 
ond and  third  extractions  in  order  to  break  the  emulsion  which  formed 
upon  the  addition  of  ether.  The  total  amount  of  ammonia  used  for 
a  5-gram  sample  varied  from  2  to  6  cc. 

THE  NORMAL  BUTYL  ALCOHOL  TEST 

The  normal  butyl  alcohol  procedure  was  that  described  by  Pro- 
fessor W.  J.  Mitchell,2  which  modifies  the  Babcock  method  by  using 
9  cc.  of  buttermilk,  2  cc.  of  normal  butyl  alcohol,  7  to  9  cc.  of  sulfuric 
acid,  and  6-2-2  minute  whirling  periods. 

THE  BABCOCK  TEST 

The  common  Babcock  method  of  testing  buttermilk  makes  use  of 
an  18-gram  sample,  about  20  cc.  of  sulfuric  acid,  and  a  10-10-5  minute 
whirling  period.  The  unsatisfactory  results  of  several  preliminary 
tests  following  this  method  led  to  a  study  of  the  following  variations 
of  the  test: 

1.  Amount  of  Acid  Used. — Comparative  tests  were  made,  using  11 
and  13.5  cc.  of  sulfuric  acid  with  a  10-gram  sample  of  buttermilk. 
(Since  the  graduated  portion  of  the  neck  of  an  18-gram  skim-milk 
bottle  is  not  of  sufficient  size  to  measure  the  fat  in  some  samples  of 
buttermilk,  it  was  decided  to  use  a  10-gram  sample  in  an  18-gram 
bottle.) 

2.  The  Time  of  Centrifuging. — A  comparison  was  made  of  the  fol- 
lowing three  periods  of  centrifuging:     (a)    20-20-10  minutes,    (b) 
10-10-5  minutes,  (c)  5-3-3  minutes. 

3.  Speed  of  the  Centrifuge. — The  effect  of  a  variation  in  the  speed 
of  centrifuging  was  determined  by  a  comparison  of  the  results  ob- 
tained at  the  following  speeds:  850,  1150,  1700  R.  P.  M. 


Methods  of  Analysis,  A.  O.  A.  C.,  1920. 
"Chicago  Dairy  Produce,  December  31,  1921. 


66 


BULLETIN  No.  248 


[January, 


EXPERIMENTAL  DATA 

A.     CONDITIONS  LIMITING  THE  USE  OF  THE  BABCOCK  TEST 
FOR  BUTTERMILK 

1.  The  Amount  of  Acid  Used. — As  the  maximum  amount  of  acid 
that  could  be  used  without  danger  of  charring  the  fat  globules  had 
been  found  to  be  13.5  to  14  cc.  (specific  gravity  1.83),  13.5  cc.  were 
selected  as  the  maximum  and  11  cc.  were  arbitrarily  chosen  as  the 
minimum  amount  of  acid  to  be  used  in  the  investigation.  The  in- 
fluence of  the  quantity  of  acid  used  is  shown  by  the  following  table. 

TABLE  1. — INFLUENCE  ON  FAT  TEST  OF  AMOUNT  OF  ACID  USED 
Speed  of  Centrifuge:    1150  R.P.M.    10-10-5  Minute  Whirling  Periods 


Sample  No.1 

11  cc.  acid 

Average 

13.5  cc.  acid 

Average 

1  

% 
.11 

% 

%        . 
.36 

% 

2  

.14 
.19 

.125 

.36 
.33 

.360 

3  

.19 

.21 

.190 

.36 

.47 

.345 

4  

.19 
.23 

.200 

.49 
.43 

.480 

5  

.16 
.16 

.195 

.43 
.47 

.430 

6  

.16 
.13 

.160 

.49 

.40 

.480 

7  

.13 

41 

.130 

.40 
54 

.400 

Average.  .  . 

.41 

.410 
.202 

.54 

.540 
.434 

'Sample  numbera  that  recur  in  other  tables  refer  to  the  same  buttermilk. 

Table  1  gives  a  comparison  of  the  results  obtained  from  running 
seven  different  samples  at  1150  R.P.M.,  using  the  two  different  amounts 
of  acid.  It  will  be  seen  that  a  much  lower  reading  was  obtained  from 
the  use  of  11  cc.  of  acid  than  when  13.5  cc.  were  used.  The  average 
percentage  of  fat  obtained  with  the  use  of  13.5  cc.  of  acid  was  more 
than  twice  the  average  test  obtained  with  11  cc.  of  acid.  These  data 
clearly  show  the  importance  of  using  the  maximum  amount  of  acid. 

2.  The  Time  of  Centrifuging. — The  following  table  presents  a 
comparison  of  the  average  tests  obtained  with  three  different  periods 
of  centrifuging  at  a  speed  of  850  R.P.M.  using  13.5  cc.  of  acid,  and 
of  the  average  tests  obtained  from  two  different  whirling  periods  at 
a  speed  of  1150  R.P.M.  using  both  11  and  13.5  cc.  of  acid. 

These  data  show  that  the  length  of  the  period  of  centrifuging  is 
of  minor  importance.  Under  the  conditions  indicated  in  Part  I  of 
the  table,  the  longer  whirling  time  resulted  in  slightly  higher  average 


1924]  MODIFIED  BABCOCK  TEST  FOE  FAT  IN  BUTTERMILK  67 

TABLE  2. — THE  EFFECT  OF  VARYING  THE  LENGTH  OF  THE  WHIRLING  PERIOD* 


Sample 
No. 

Whirling  period 
(minutes) 

Speed 
of 
centrifuge 

Acid 
used 

5-3-3 

10-10-5 

20-20-10 

Part  I 

4 

.380 
.405 
.500 
.695 
.380 
.365 
.454 

.440 
.405 
.530 
.750 
.370 
.355 
.475 

.410 
.415 
.560 
.730 
.450 
.420 
.497 

R.  P.  M. 
850 

cc. 
13.5 

6  

7  

8 

9  

10  

Average.  .  . 

Part  II 

1.  . 

.360 
.345 
.480 
.430 
.480 
.530 
.438 

.335 
.345 
.470 
.430 
.480 
.540 
.433 

R.  P.  M. 
1150 

CO. 

13.5 

2  

3  

4  

5  

7  

Average.  .  . 

Part  III 

1.  . 

.125 
.190 
.200 
.195 
.160 
.130 
.410 
.201 

.170 
.205 
.290 
.255 
.290 
.130 
.495 
.262 

R.  P.  M. 
1150 

cc. 
11 

2  

3  

4  

5..  . 

6  

7  

Average.  .  . 

1The  values  given  in  this  table  are  the  averages  of  duplicate  tests, 
greatest  difference  between  duplicates  was  0.07  percent. 


The 


fat  percentages.  By  comparing  the  averages  given  in  Parts  I  and  II 
it  will  be  seen  that  the  longer  whirling  periods  gave  higher  results 
only  at  the  lower  speed  and  even  then  the  increase  was  slight.  The 
only  really  appreciable  increase  in  the  test  obtained  from  a  longer- 
whirling  period  is  shown  by  the  figures  given  in  Part  III ;  these  show 
that  when  the  minimum  amount  of  acid  (11  cc.)  was  used  the  longer 
whirling  period  resulted  in  an  increase  in  the  average  reading  from 
0.201  to  0.262  percent,  an  increase  of  about  one-third.  However,  by 
referring  to  Part  II  of  the  table,  it  will  be  seen  that  when  13.5  cc. 
of  acid  were  used  at  a  speed  of  1150  R.P.M.  as  high  results  were  ob- 
tained from  10-10-5  minute  periods  of  centrifuging  as  from  20-20-10 
minute  periods. 

3.  The  Speed  of  Centrifuging. — To  determine  whether  or  not  in- 
creasing the  speed  of  centrifuging  would  increase  the  reading,  the 
same  samples  were  run  at  850  R.P.M.  and  1150  R.P.M.  with  10-10-5 
minute  whirling  periods,  and  at  1150  and  1700  R.P.M.  with  20-20-10 
minute  whirling  periods.  In  all  cases  13.5  cc.  of  sulfuric  acid  (the 
amount  found  to  give  best  results)  were  used.  It  was  found  that 


68 


BULLETIN  No.  248 


[January, 


when  the  speed  of  the  centrifuge  was  increased  to  1700  R.P.M.  several 
of  the  test  bottles  were  broken  by  the  increased  pressure  exerted  upon 
them.  For  this  reason  and  because  it  was  thought  that  any  increase 
in  reading  to  be  obtained  from  the  higher  speed  would  be  more  no- 
ticeable with  20-20-10  minute  whirling  periods  than  with  the  shorter 
ones,  it  was  deemed  advisable  to  use  the  high  speed  only  with  the 
longer  whirling  period. 

TABLE  3. — THE  EFFECT  OF  VARYING  THE  SPEED  OF 


Sample 
No. 

Speed  of  centrifuge 

Whirling 
period 

Amount  of 
acid  used 

850  R.  P.  M. 

1150  R.P.M. 

1700  R.  P.  M. 

4.  .  . 

% 
.440 
.425 
.530 
.750 
.370 
.355 
.478 

.430 
.400 
.540 
.690 
.390 
.350 
.467 

% 

minutes 
10-10-5 

13.5  cc.  in 
all  cases 

6  

7  

8  

9  

10.  . 

Average. 

1  

.360 
.345 
.470 
.430 
.480 
.540 
.437 

.355 
.325 
.450 
.435 
.490 
.555 
.435 

20-20-10 

13.5  cc.  in 
all  cases 

2  

3. 

4  

5  

7  

Average. 

1The  values  given  in  this  table  are  the  averages  of  duplicate  tests.  The 
greatest  difference  between  duplicates  was  0.05  percent. 

The  data  in  Table  3  show  that  when  using  13.5  cc.  of  acid  and  a 
10-10-5  minute  whirling  period  as  high  results  were  obtained  with  a 
speed  of  850  R.P.M.  as  with  1150  R.P.M.  Increasing  the  speed  to 
1700  R.P.M.  resulted  in  no  higher  readings  than  those  obtained  at  1150 
R.P.M.,  even  with  the  20-20-10  minute  whirling  periods. 


B.    A  COMPARISON  OF  THE  BABCOCK,  NORMAL,  BUTYL  ALCOHOL,  AND 

ROESE  GOTTLIEB  METHODS  FOR  DETERMINING  THE  PERCENTAGE 

OF  FAT  IN  BUTTERMILK 

As  a  result  of  the  foregoing  data,  the  following  modification  of  the 
Babcock  method  was  decided  upon  for  a  comparison  with  the  normal 
butyl  alcohol  and  Roese-Gottlieb  methods  of  determining  the  fat  in 
buttermilk:  10-gram  sample;  13.5  cc.  of  acid  (measured  from  a  bu- 
rette) ;  10-10-5  minute  whirling  periods ;  1150  R.  P.  M.  The  results 
are  given  in  Table  4. 

A  comparison  of  the  results  obtained  by  the  Babcock  and  Roese- 
Gottlieb  methods  shows  that  the  Babcock  results  are  always  less  than 
those  of  the  Roese-Gottlieb.  It  was  noticed  also  that  the  difference 
between  the  two  was  fairly  constant,  being  about  0.2  of  one  per- 
cent of  fat.  (The  average  difference  between  the  results  obtained  on 
the  12  samples  is  0.2047  of  one  percent).  In  other  words,  practically 


1984] 


MODIFIED  BABCOCK  TEST  FOR  FAT  IN  BUTTERMILK 


69 


0.2  of  one  percent  of  the  fat  in  buttermilk  is  held  so  tightly  by  the 
milk  constituents  that  the  combined  action  of  the  acid  and  the  centri- 
fugal force  fails  to  liberate  it.  The  same  fact  is  true  in  testing  whole 
milk,  in  which  test  a  correction  is  made  for  the  approximate  0.2  of 
one  percent  fat  that  does  not  rise  in  the  neck  of  the  bottle,  by  reading 
the  fat  column  to  the  top  of  the  meniscus. 

By  using  0.2  as  a  correction  factor  and  adding  to  the  results  ob- 
tained by  the  Babcock  method,  a  value  is  obtained  which  is  closely 
comparable  to  that  obtained  by  the  Roese-Gottlieb  method. 

In  addition,  the  data  in  Table  4  confirm  the  work  of  Professor 
Mitchell,  already  referred  to,  in  that  the  results  obtained  by  the  nor- 
mal butyl  alcohol  method  correspond  closely  with  those  obtained  by 
chemical  analysis. 

TABLE  4. — A  COMPARISON  OF  THE  MODIFIED  BABCOCK,  NORMAL  BUTYL  ALCOHOL, 

AND   KOESE-GOTTLIEB   METHODS   FOR   DETERMINING   THE    FAT   IN   BUTTERMILK 


Sample 
No. 

Babcock 

Average 

Babcock 
plus  .2 

N.  B. 
alcohol 

Average 

Roese- 
Gottlieb 

Average 

1  

% 
.36 

% 

% 

% 
.58 

% 

% 
.590 

% 

2 

.36 
36 

.360 

.56 

.58 
.53 

.580 

.572 
.545 

.5810 

3   .    . 

.33 
.49 

.345 

.545 

.53 
.69 

.530 

.544 
.667 

.5445 

4  

.47 
.43 

.480 

.68 

.68 
.60 

.685 

.664 
.628 

.6655 

5 

.43 
49 

.430 

.63 

.60 

.68 

.600 

.626 
.698 

.6270 

6  

.47 
.40 

.480 

.68 

.68 
.54 

.680 

.685 
.596 

.6915 

7  

.40 
.54 

.400 

.60 

.54 
.72 

.540 

.598 
.759 

.5970 

8  

.54 
.71 

.540 

.74 

.72 
.94 

.720 

.772 
.904 

.7655 

9 

.67 
.39 

.690 

.89 

.94 
.56 

.940 

.897 
.570 

.9005 

10  

.39 

.35 

.390 

.59 

.55 
.56 

.555 

.570 
.566 

.5700 

11  

.35 

.44 

.350 

.55 

.56 
.62 

.560 

.554 
.662 

.5600 

12 

.44 
1  29 

.440 

.64 

.62 
1  50 

.620 

.645 
1  485 

.6535 

1.29 

1.29 

1.49 

1.50 

1.50 

1.500 

1.4925 

Average. 

.516 

.716 

.709 

.7207 

DISCUSSION  OF  THE  TESTS 

The  results  of  this  work  indicate  that  the  amount  of  acid  added  is  the 
most  important  factor  to  be  considered  in  using  the  Babcock  test  for  butter- 
milk. Another  very  important  factor,  which  does  not  appear  in  the  data 
presented,  is  the  construction  of  the  skim-milk  bottle  used.  Many  bottles 


70  BULLETIN  No.  248 

are  so  constructed  that  they  "choke  up"  very  easily  at  the  base  of  the 
graduated  capillary.  A  slight  constriction  at  this  opening  will  result  in 
preventing  some  of  the  fat  from  rising  into  the  neck  of  the  bottle.  By 
carefully  selecting  the  test  bottles  and  eliminating  those  that  repeatedly 
"choked  up"  this  difficulty  was  lessened.  For  this  reason,  in  selecting 
bottles  that  are  to  be  used  in  the  test,  care  should  be  taken  to  choose  those 
that  have  the  graduations  close  together,  as  this  indicates  a  wide  capillary. 
Too  much  emphasis  cannot  be  laid  upon  the  need  of  a  test  bottle  that  is 
properly  constructed  for  the  testing  of  buttermilk. 

The  normal  butyl  alcohol  test  also  is  somewhat  handicapped  by  the 
lack  of  a  desirable  test  bottle;   otherwise  the  method  is  very  successful. 

CONCLUSIONS 

1.  The  amount  of  acid  used  has  a  very  important  effect  upon  the  re- 
sults obtained  in  the  Babcock  method  of  testing  buttermilk. 

2.  The  extension  of  the  whirling  period  beyond  the  10-10-5  minute 
periods  has  no  appreciable  effect  upon  the  result  obtained  in  the  Babcock 
method  of  testing  buttermilk. 

3.  Increasing  the  speed  of  the  centrifuge  above  900  to  1000  revolu- 
tions per  minute  will  not  increase  the  readings  obtained  in  the  Babcock 
method  of  testing  buttermilk. 

4.  With  the  proper  modifications  of  the  Babcock  test  and  with  the 
addition  of  a  correction  factor  of  0.2,  results  can  be  obtained  that  will  con- 
form closely  to  the  Roese-Gottlieb  determination. 

5.  The  normal  butyl   alcohol  method   of  testing  buttermilk   for  fat 
checks  closely  with  the  Roese-Gottlieb  method. 

DIRECTIONS  FOR  OPERATING  THE  MODIFIED  BABCOCK  TEST  FOR 

BUTTERMILK 

As  a  result  of  this  investigation,  the  following  modification  of  the  Bab- 
cock test  for  determining  the  fat  in  buttermilk  is  presented : 

1.  If  the  sample  contains  visible  granules  of  butter  fat,  strain  it  thru  cheese- 
cloth, as  floating  granules  of  butter  are  not  indicative  of  the  exhaustiveness  of 
churning. 

2.  Thoroly  mix  the  sample. 

3.  By  means  of  a  10-gram  Mojonnier  pipette,  measure  10  grams  of  the  but- 
termilk to  be  tested  into  a  skim-milk  bottle  (use  a  0.5-percent  bottle  if  possible). 

4.  Add  13.5  cc.  of  commercial  sulftirir   acid    (having  a  specific  gravity  of 
1.82-1.83)   from  a  burette  or  14  ce.  from  an  acid  measure,  and  mix  well. 

5.  Centrifuge  at  a  speed  of  about  1000  R.P.M.  for  10  minutes. 

6.  Add  enough  hot  soft  water  to  raise  the  mixture  in  the  bottle  to  the  point 
where  the  graduated  neck  is  joined  to  the  shoulder  of  the  bottle.     Whirl  10  minutes. 

7.  Finish  filling  bottle  with  hot  soft  water  and  whirl  for  5  minutes. 

8.  Allow  to  remain  5  minutes  in  a  hot-water  bath  having  a  temperature  of 
135-140°   F. 

9.  Read  to  top  of  meniscus  and  multiply  the  result  by  1.8.      (The  fat  col- 
umn should  be  a  dark  amber  color.     If  it  is  a  straw  yellow  color,  the  amount  of 
acid  used  should  be  increased.) 

10.  Add  the  correction  factor  of  0.2. 


UNIVERSITY  OF  ILLINOIS-URBANA 


